Semiconductor devices and liquid crystal display devices are produced by means of the so-called photolithography technique in which a pattern formed on a mask is transferred onto a photosensitive substrate. The exposure apparatus, which is used in the photolithography step, includes a mask stage for supporting the mask and a substrate stage for supporting the substrate. The pattern on the mask is transferred onto the substrate via a projection optical system while successively moving the mask stage and the substrate stage. In recent years, it is demanded to realize the higher resolution of the projection optical system in order to respond to the further advance of the higher integration of the device pattern. As the exposure wavelength to be used is shorter, the resolution of the projection optical system becomes higher. As the numerical aperture of the projection optical system is larger, the resolution of the projection optical system becomes higher. Therefore, the exposure wavelength, which is used for the exposure apparatus, is shortened year by year, and the numerical aperture of the projection optical system is increased as well. The exposure wavelength, which is dominantly used at present, is 248 nm of the KrF excimer laser. However, the exposure wavelength of 193 nm of the ArF excimer laser, which is shorter than the above, is also practically used in some situations. When the exposure is performed, the depth of focus (DOF) is also important in the same manner as the resolution. The resolution R and the depth of focus δ are represented by the following expressions respectively.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
In the expressions, λ represents the exposure wavelength, NA represents the numerical aperture of the projection optical system, and k1 and k2 represent the process coefficients. According to the expressions (1) and (2), the following fact is appreciated. That is, when the exposure wavelength λ is shortened and the numerical aperture NA is increased in order to enhance the resolution R, then the depth of focus δ is narrowed.
If the depth of focus δ is too narrowed, it is difficult to match the substrate surface with respect to the image plane of the projection optical system. It is feared that the margin is insufficient during the exposure operation. Further, the optical part material, which is usable for the exposure light beam that has the increasingly shortened wavelength, is restricted. From the viewpoints as described above, the liquid immersion method has been suggested, which is disclosed, for example, in International Publication No. 99/49504 and Japanese Patent Application Laid-open No. 10-303114 as a method for substantially shortening the wavelength of the exposure light beam after passing via the projection optical system and widening the depth of focus. In this liquid immersion method, the space between the lower surface of the projection optical system and the substrate surface is filled with a liquid such as water or any organic solvent to form a liquid immersion area so that the resolution is improved and the depth of focus is magnified about n times by utilizing the fact that the wavelength of the exposure light beam in the liquid is 1/n as compared with that in the air (n represents the refractive index of the liquid, which is about 1.2 to 1.6 in ordinary cases).
As schematically shown in FIG. 18, an edge area E of a substrate P is sometimes subjected to the exposure as well in the case of the exposure apparatus which adopts the liquid immersion method. In such a situation, a portion of the projection area 100 protrudes to the outside of the substrate P, and the exposure light beam is also radiated onto a substrate table 120 for holding the substrate P. In the case of the liquid immersion exposure, the liquid immersion area of the liquid is formed so that the projection area 100 is covered therewith. However, when the edge area E is subjected to the exposure, then a part of the liquid immersion area of the liquid protrudes to the outside of the substrate P, and the liquid immersion area is also formed on the substrate table 120. When various measuring members and/or measuring sensors are arranged around the substrate P on the substrate table 120, the liquid immersion area is also formed on the substrate table 120 in some cases in order to use the measuring members and/or the measuring sensors. When a portion of the liquid immersion area is formed on the substrate table 120, then the liquid may remain on the substrate table 120 highly possibly, and the following possibility arises. That is, for example, the environment (temperature, humidity), in which the substrate P is placed, may be varied as a result of the vaporization of the remained liquid, the substrate table 120 may be thermally deformed, the environment of the optical paths for various measuring light beams to measure, for example, the position information about the substrate P may be varied, and the exposure accuracy may be lowered. Further, the following possibility arises as well. That is, the water mark (trace of water) may remain after the vaporization of the remained liquid, which may result in the factor of the pollution of, for example, the substrate P and the liquid, and which may result in the factor of the error concerning various types of measurements.